Vaccination can protect individuals from infectious disease.
Poliomyelitis (polio) is a highly infectious viral disease that can cause irreversible paralysis and other severe complications.
Suggest the primary biological component of a typical polio vaccine.
Describe the role of T-lymphocytes in the development of immunity against a viral pathogen such as the poliovirus.
The table below shows the recorded annual number of polio cases in a certain country around the time a national vaccination programme was introduced:
YearNumber of cases195343,0001955 (vaccine introduced)35,000195618,00019601,400\begin{array}{|c|c|} \hline \text{Year} & \text{Number of cases} \\ \hline 1953 & 43,000 \\ \hline 1955 \text{ (vaccine introduced)} & 35,000 \\ \hline 1956 & 18,000 \\ \hline 1960 & 1,400 \\ \hline \end{array}Year19531955 (vaccine introduced)19561960Number of cases43,00035,00018,0001,400Calculate the percentage decrease in recorded cases of polio between 1955 and 1960.
A student wants to use the percentage decrease from (b)(i) to draw conclusions about the effectiveness of the polio vaccine. Another student argues that 1956 would be a better starting year for the calculation.
Suggest two reasons why 1956 might be a better starting year than 1955.
In the late 1990s, the number of polio cases in this country fell to fewer than 5 per year. Suggest one way in which the yyy-axis scale of a trend graph covering 1953 to 2000 could be changed so that fluctuations in both high-case and low-case years are visible.
